Roll Groove Research Articles

Experimental study on the surface defects of materials in bar rolling with a processing map applicable to billet-to-oval groove rolling

This paper proposes a systematic method for detecting surface defects (SDs) on specimens by performing a pilot hot (850°C–950°C) bar rolling test and suggests a processing map for billet-to-oval groove pass in bar rolling mills. Unlike previous studies, the specimens for the rolling test were prepared such that the billet surface became the surface of the specimens. A series of the rolling tests were performed at different temperature and area reduction ratios. Physical-chemical nondestructive testing was employed to detect SDs in the specimens before and after the rolling test. The depth of the SDs of the rolled specimens was measured using an optical microscope. The results revealed that the SDs depended both on the rolling parameters (temperature and reduction ratios) and the contact condition between the specimen and the roll groove during rolling, which is one of the characteristics of bar rolling that distinguishes it from flat rolling. The decrease in temperature caused an increase in the defect depth above the appropriate reduction ratio of 24.61% when the part of the specimen was in contact with the roll shoulder curve and the relief line of the oval roll groove. The proposed processing map presents a guiding path for operators in actual bar rolling mills to quickly determine a rolling condition (combination of temperature and reduction ratio), avoid SDs, and minimize defect depth within an acceptable range.

Inner Surface Morphology and Roughness Evolution of Pilgering Thick-Walled Tubes.

A hot-working die steel thick-walled tube Pilger rolling test was carried out using an LG40 Pilger mill, and the morphology and roughness evolution of the inner surface were examined using a white-light interferometer. The experimental results showed that micro-wrinkles formed on the basis of the original inner surface morphology, the altitude difference (Sz) between the peaks and valleys of the inner surface profile increased from 3.18 to 3.686 μm, and Sa increased from 0.722 to 0.892 μm in the diameter reduction zone. As the tube continued to feed into the wall thickness reduction zone, the micro-wrinkles gradually flattened, Sz and Sa were decreased to 1.625 and 0.174 respectively, and Sa maintained a slight fluctuation of 0.174~0.2 μm in the final sizing zone. From the diameters of the roller groove and taper of the mandrel, the three-dimensional strain of the tube in the wall thickness reduction zone was calculated, and the strain state of the tube in the complete deformation zone could be analyzed by finite element simulations. We found that in the diameter reduction zone, the inner surface was not supported by the mandrel and was free, while micro-wrinkles formed under circumferential compressive strain. In the wall thickness reduction zone, the deformation of the inner surface was controlled by the mandrel, and the micro-wrinkles were gradually flattened by radial compressive strain. The ratio of radial to circumferential strain was the key to flattening the micro-wrinkles, and when the ratio increased, the inner surface roughness (Sa) was reduced to 0.174 μm. In the sizing zone, the radial and circumferential strains were small, and the inner surface roughness showed no obvious fluctuation.

Failure behavior of a roller in automotive flywheel manufacturing

The failure behavior of a carburized 18CrNiMo7-6 steel roller from a roll forming mill used to manufacture automotive flywheels is investigated. Microstructural observations using optical and scanning electron microscopy are carried out, and the hardness determined using a Vickers hardness testing machine. The carburized layer is mainly comprised of fine tempered martensite, small carbides and retained austenite. The depth of the carburized layer around the roller groove is thinner than the required standard. The decrease in microhardness with increasing distance from the surface to the core is found to be due to the different carbon concentrations. However, a pronounced variation of the microhardness value is detected around the roller groove surface. This is related to the formation of an inhomogeneous microstructure during quenching after the carburizing process. The results indicate that the crack nucleates at the bottom surface of the roller and propagates along the direction vertical to the roll forming with a transgranular character.

THE EFFECT ROLL ROAD OF ROUGHNESS ON THE PERFORMANCE OF NUTMEG

The process of flattening nutmeg is one of the steps that must be carried out before it becomes a dish that can be enjoyed or marketed. The dimensions of the fruit and the relatively unequal surface structure between each other can hinder the flattening process if done in a conventional way. The addition of a profile to increase the surface roughness on the rollers of the flattening machine will affect the performance of the flattening process using a contra-rotary roll type flatter machine. The purpose of this study was to determine the effect of adding a surface profile to increase roller roughness on the flattening performance of nutmeg. The research was conducted by experiment where the profile was made with a pattern of transverse grooves on the rollers using variations in the number of grooves including 4; 6; and 8. Machine performance analysis includes the duration of the flattening process and the physical characteristics of the fruit being processed. The results showed that the maximum weight difference occurred in the 6 groove roller variation of 4.8 g with the highest thickness difference in the 6 groove variation of 3.35 mm. The fastest duration is shown in groove 8 variation of 1.98 sec. The lowest use of electric power is found in the variation of the 8 roller groove of 35.64 W.

Incremental rolling forming process to fabricate surface micro-grooves

The fabrication of functional micro-structures at sheet surface has a wide range of applications in noise reduction, friction reduction, heat and mass transfer, etc. By integrating the conventional rolling forming and the incremental sheet forming process, a flexible and widely applicable incremental rolling forming process was proposed in the present work to fabricate surface micro-grooves. First, a rolling tool which has hemispherical ring convex on the roller and the convex height is much higher than the height of forming groove was designed and manufactured. Then, a series of incremental rolling tests on titanium alloy (TA1) were carried out by using self-designed rolling tools, with varying roller size, rolling depth and feed rate. The results show that continuous micro-grooves with good dimensional consistency were prepared on the surface of the plate. Furthermore, by investigating rolling force and groove size after rolling, it was found that the rolling depth have significant effects on the micro-groove formation and only localized material flow is occurred at the grooved region. Compared with the traditional rolling process, the incremental rolling process has the advantages of low rolling force and adjustable groove spacing, which is conducive to the subsequent processing of the sheet.

Influence of process layouts of multi-roll solid-liquid cast-rolling bonding process on circumferential performance uniformity during fabricating metal cladding materials

The twin-roll casting (TRC) process is typically used to fabricate laminated metal cladding strips with rectangular cross-sections, and it has the advantages of short flow, low energy consumption, green environmental protection, etc. Recently, a twin-roll solid-liquid cast-rolling bonding (TRSLCRB) process was proposed based on the TRC process to fabricate metal cladding materials with round cross-sections. However, the nonuniformity of heat transfer and mass transfer along the circumferential direction finally influences the performance uniformity. Therefore, a multi-roll solid-liquid cast-rolling bonding (MRSLCRB) process was proposed integrating cast-rolling bonding technology and multi-roll groove rolling technology. The steady-state thermal resistance network was established, and the influences of nominal roll radius, groove radius, and molten pool height on the heat transfer and mass transfer were studied systematically. 3-D steady-state thermal-fluid coupled simulation models of twin-roll, three-roll, and four-roll layouts were established. The results indicate that increasing casting roll number can improve the nominal cast-rolling velocity, service life of the casting roll, temperature uniformity, strain uniformity, and strain rate uniformity through regulating the heat transfer and mass transfer. Considering the manufacturing feasibility, the MRSLCRB equipment based on the three-roll layout was designed. Cu/steel cladding bars with uniform circumferential performance were fabricated, and the forming mechanism was revealed. The multi-field coupled analysis method provides a way to control heat and mass transfer uniformity, and the successful attempts of various typical metal cladding materials inspire exploring new forming processes.

Modernization of screw rolling technology in a multi-roll mill

Analysis of the screw rolling process showed that change in axial speed of the roll along the length of the roll groove of cross rolling mill does not correspond to the required character of change in the speed of deformed billet. The process proceeds under intense axial compression, as a result of which a significant part of the metal crimped in the contact zone is displaced into the inter-roll area. It is shown that direction of the axial force in the corresponding zone of the roll groove depends on the value of inclination angle of the considered roll section generatrix to the rolling axis. The proposed modernization of screw rolling technology makes it possible to carry out deformation of the billet under the influence of intra-focal axial tension. The task is accomplished by rolls calibration when at the beginning there is a ridge section of the roll on which the axial force is directed against rolling direction; and behind it, a pulling one, on which the direction of the axial force coincides with rolling direction. Such a scheme of the axial forces action in the zone of intensive billet reduction creates the most favorable conditions for the metal flow in axial direction. A technical solution is proposed for the implementation of the stage of the billet gripping by rolls, and description of this stage and the process stationary phase is given. The cardinal change in the billet deformation condition after modernization makes it possible to reduce the power load on the work rolls, increase their efficiency and reduce energy costs during rolling. This will ensure the rolling of a solid billet in a roughing mill with a higher stretch, create the preconditions for expanding the size and grade assortment when obtaining rods in radial-displacement rolling mills and at production of pipes in rolling lines with the Assel mill. The range of finished products can be significantly expanded due to the production of thin-walled highprecision pipes.

Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

Investigation structure and properties of wire from the alloy of AL-REM system obtained with the application of casting in the electromagnetic mold, combined rolling-extruding, and drawing

The paper presents the results of studies of the structure and properties of a wire with a diameter of 0.5 mm from an alloy of the Al-REM system with a rare-earth metal content of 7–9%. Wire obtained as a result of the implementation of the technology of its manufacture using the methods of casting into an electromagnetic mold (EMM), continuous extruding, and drawing. The rheological properties of the metal of continuously cast round billets from the experimental alloy obtained using an electromagnetic mold are determined. The modeling and analytical assessment of the possibility of carrying out the process of combined rolling-extruding (CRE) of such billets in a closed box-type roll groove of a continuous extruding unit are carried out. The features of metal shaping have been studied. The temperature-speed and technological parameters were found at which the CRE process can be carried out in a stable mode of operation. Data have been obtained for the forces acting on the die and rolls during rolling-extruding. The results of experimental studies of the process of obtaining longish deformed semi-finished products from an experimental alloy on the laboratory unit CRE-200 and the pilot plant unit CRE-400 are presented. The structure of the metal has been studied; data on the ultimate tensile strength, yield strength, relative elongation, and electrical resistance of hot-extruded rods and wires in cold-worked and annealed states have been obtained. It was found that the proposed processing modes make it possible to obtain by the method of combined rolling-extruding rods with a diameter of 9 mm in industrial conditions from longish billets with a diameter of 18 mm, cast by means of EMM. Wire in a cold-deformed and annealed state with a diameter of 0.5 obtained by drawing from the rods with a diameter of 9 mm from an experimental alloy of the Al-REM system containing 7–9% rare-earth metals with the required physical and mechanical properties.

A computational method for pass design of the four-roll rolling process for sizing of round sections

The four-roll rolling process (4RP) enables the further evolution of sizing processes in rolling mills for round sections. The well-known advantages of the three-roll process over the two-roll process can be further improved using the 4RP. The participation of four rolls in the deformation zone instead of three or two leads to a significant increase in deformation efficiency. The present work shows a pass design method for pass sequences in the four-roll rolling process. Here, three basic types of roll groove geometries are discussed: the flat groove, the non-opened single-radius groove, and a tangentially opened type of a single radius groove. Based on a predefined cross-sectional evolution, grooves are found numerically to satisfy two conditions, i.e., the cross section of the rolled section and the groove filling criterion. The equations of the equivalent pass method, together with a suitable model for lateral spread and the geometric equations of the groove are solved by nonlinear optimization to minimize the sectional and filling errors of a specific pass. Combined for several rolling passes, a complete pass design can be carried out for the reduction of a specified initial section to a final section. The presented results show, how a pass design method for the four-roll rolling process can be constructed. The newly developed model is implemented in a software solution for pass design and analysis of full section rolling mills. An exemplified pass design is discussed to show the possibilities and limitations of the new model.

Study of the process of formation of tubes end sections during longitudinal rolling in grooves formed by a different number of rolls

The work substantiates the relevance and highlights the degree of development of the research topic. The main advantages and disadvantages of the process of rolling hollow billets with the use of modern longitudinal rolling mills with 2 and 3 roll grooves are noted. With the help of physical and computer modeling, a study of the process of longitudinal rolling of pipes using 2 and 3 roll passes was carried out, for the formation of end sections (scrap). Established and numerically reflected the relationship between the size of the reduction of passes of a continuous rolling mill with 3-roll and 2-roll stands and the length of the end sections of the pipes. It is clear that the use of 3 rolls, forming a groove, allows to reduce the total end cut by 1.5 times, in contrast to 2 rolls. It has been determined that the main technological factors influencing the formation of the end sections are the ratio of the external diameter to the wall thickness of the strip (D/S), the reduction along the wall thickness, the elongation ratio, and the number of rolls required to form the groove. An empirical formula has been obtained for calculating the length of the end trim, which makes it possible to evaluate the influence of the number of rolls in the stand, the D/S ratio and the stretch ratio.

Study on the forward slip of cup with variable wall thickness during roll forming

Based on the principle of plastic forming, the metal flow of cup with variable wall thickness during roll forming is analyzed, and the formula of its coefficient of forward slip is derived. By comparing with the numerical simulation results, the correction formula of the coefficient of forward slip at the rim of roller is obtained. The correction formula is verified by experiment. The results show that the error between the theoretical and experimental value is 4.5%, and the agreement between them is good. This research provides a basis for the design of the roller groove for the roll forming of cup with variable wall thickness.

Hybrid modeling and analysis of multidirectional variable stiffness of the linear rolling guideway under combined loads

In the working process of high-speed multiaxis machine tools, inertial loads due to high feed acceleration and time-varying gravity loads due to changing configuration of multiaxis structure result in time-varying complex loads applied to linear rolling guideway. Existing models cannot efficiently represent the effect of complex loads on multidirectional stiffness variation of linear rolling guideway. In this paper, a hybrid model of multidirectional stiffness of linear rolling guideway and the solving algorithm are proposed. The complex loading conditions of linear rolling guideway in high-speed multiaxis machine tool structure are considered. And contact flexibilities between rolling balls and grooves are modeled with the effect of elastic deformations of runner block and rail. The proposed model can calculate the multidirectional stiffness with high accuracy. Meanwhile the differences between the stiffness characteristics in different directions are represented correctly. The variations of multidirectional stiffness of linear rolling guideway under time-varying combined loads are analyzed. This study provides an effective way to comprehensively evaluate the stiffness characteristics of linear rolling guideway which can contribute to the dynamic analysis and active design of high-speed machine tool structure.

Tooling design–related spatial deformation behaviors and crystallographic texture evolution of high-strength Ti-3Al-2.5V tube in cold pilgering

Cold pilgering has been considered as the preferred rolling fabrication technology for difficult-to-deform tubular materials such as high-strength titanium alloy tubes. However, the tooling geometry may induce complex deformation and significantly influence crystallographic texture which is closely related to the dimension assuring and properties tailoring of tube products. In this study, taking high-strength Ti-3Al-2.5V tubes as the case material, the tooling design–related spatial deformation behaviors and crystallographic texture evolution of tube in cold pilgering are focused. A macro-meso scaled computation platform is established by combining the three-dimensional finite element (3D-FE) model with the viscoplastic self-consistent (VPSC) crystal plasticity model to predict both the inhomogeneous macrodeformation and microtexture evolution in cold pilgering. Two basic tooling parameters in pilgering, viz., E1 representing exponent of roller groove curve and mandrel curve and E2 representing exponent of groove clearance, are chosen as the design variables. The cold pilgering under different tooling parameters are simulated and analyzed. The results show that (1) The rolling force decreases with the increase of E1 , while the effect of E2 on the rolling force is not significant, and smaller E1 and larger E2 have advantage for preventing surface defects of the tube product; (2) The E1 of 2.8 and E2 of 2.0 are more conducive to the wall thinning–dominated deformation of tube; (3) Taking the contractile strain ratio (CSR) as an indicator for characterizing crystallographic texture–related mechanical properties, the appropriate values of E1 and E2 for desirable radial texture of tube product are obtained.

Forming of Small Projection on Roll-Cast A356 Strip by Cold Rolling and Small Groove on PET Plate Using A356 Die

A small projection with a height and width of about 40 and 50 µm, respectively, was formed on a twin-roll-cast A356 aluminum alloy sheet by cold rolling at a rolling speed of 0.5 m/min. This projection was then used as a die to form a groove with a depth and width of about 40 and 50 µm, respectively, on a polyethylene terephthalate plate by pressing.

Experimental studies on Zr–1%Nb alloy properties in technological conditions of cold pilger tube rolling process

The paper presents the results of research on the rheological properties of the Zr–1%Nb alloy, obtained for the strain parameters corresponding to the cold rolling tube process in a pilger mill. The studies were carried out under conditions of continuous, discontinuous and variable load in the GLEEBLE 3800 metallurgical processes simulator, according to the program developed on the basis of conditions occurring in the actual technological process. The influence of the strain, strain rate, plastic deformation thermal effect and the Bauschinger effect on changes in the flow stress was determined. Recommendations for division of the alloy strain distribution over the length of the deformation zone in the pilger roll grooves is presented.

Forming defect control and optimization of multi-step spinning thickening process considering the variation of spinning gap

Spinning thickening is a novel metal-bulk forming technology for sheet metal, which gains successful applications in the net-shape manufacture of the structural parts with thin web plates and thick rims in automobile industry. However, through-process design of the forming scheme considering the possible variation of relative position of the plate is still lacking. To this end, the instantaneous stress-strain distribution of the plate, the bending force of the plate, and the order of the metal filling into roller groove were analyzed. Additionally, forming quality of the Eigen-structure with different spinning gaps was studied and quantitatively evaluated by experiments and FE simulation. It is found that pit, flash, hump, and depression are the dominant forming defects that influence the surface quality and performance of the parts. With the increase of positive spinning gaps, the area of the pit increases firstly and then decreases. With the increase of the absolute value of negative spinning gaps, the area of the pit increases continuously. By employing weighting method, a new index is proposed to evaluate the combined forming quality of the Eigen-structure. In addition, a phenomenological model was established for characterizing the correlation between the spinning gap and the quality index. Finally, taking the variation of spinning gap into consideration, process optimization of a two-step spinning thickening process was carried out under the constraint of multiple defects. The optimized range of spinning gap was obtained and experimentally validated. Results show that the quality of thick rim is improved by utilizing the optimized scheme and the target parts were formed with high quality under the reasonable range of spinning gap.

Study on Multi-Step Spinning Process for Disk-Like Part with Thickened Rim

This paper studies the process of a five-step spinning to thicken the edge of the disc-like part. By using finite element simulation and experiment, the sectional shape and flow-line distribution of the rim were studied. The results showed that the flow lines of the cross-section of the formed part are distributed along the shape of the part. The disc-like part with thickened rim can be well formed by a multi-step spinning process. A large bottom radian of roller groove can lead a folding in the first step and a reduced r can overcome the folding. An over-small angle αin step 2 will lead a pit defect, it can be solved by increasing the angle.

Statics analysis and experimental study on the bi-stable self-amplifying force clutch of hybrid electric vehicles

At present, hybrid electric buses are mainly used for urban buses, which work in two conditions for a long time, such as clutch separation and clutch engagement, but the mono-stable clutch cannot meet the needs. According to the working demands of the clutch, this thesis puts forward a new bi-stable clutch configuration used in hybrid electric vehicles, and then its working principle is described, which realizes self-amplifying force effect and solves self-locking defects through the structure of double-disc steel ball rolling groove mechanism. Based on statics analysis theory, the statics analysis was carried out on the back-and-forward rotating pressure plate, the clutch’s rear end cover and master pin. Then a bi-stable clutch test bed is set up in order to conduct the clutch’s bearing torque, separation thoroughness, heat load test and service life test. Its conclusion provides a good foundation for the further optimal design of the bi-stable clutch.

Minimzing the value of axial forces in the cold tube rolling mills

The aim. Subsequent development of procedure for calculation of the kinematic parameters of the process of tube deformation in the cold tube pilger roll rolling mills with purpose of decreasing the value of axial forces. Methods. The new method (procedure) for the choice of the rational relationship of values of the forced rolling radius and the roll barrel radius in the mill KPW (method of the work minimum) had been assumed as the basis of development of the procedure for calculating the kinematic parameters of the tube deformation process in the cold tube pilger roll rolling mills. The outcome. The main dependencies known for now, which are used for calculating the value of the natural rolling radius and the roll barrel radius had been considered in the present paper, as well as the main practice used for decreasing the value of axial forces in the CTR mills. A procedure had been proposed for calculating the kinematic parameters of the tube deformation process in the mills of the cold tube pilger roll rolling (the method of the work minimum). Basing on the outcomes of industrial exploitation of the given method one drew the conclusion as to effectiveness of the proposed procedure. The scientific novelty. Basing on existing dependencies, the development of procedure had been proposed for calculating the rational relationship of the forced rolling groove radius and the roll barrel radius in the cold tube rolling mills. The procedure is based on the intimate analysis of axial forces, which are determined proceeding from all the basic parameters of the process. The practical importance. The given method allows optimizing not only the maximum values of axial forces at the direct and reverse stroke of the stand, but also the intensity of forces distribution along the cone of deformation. The method (procedure) had been used while calculating a number of roll pass designs for rolling tubes of titanium alloys in the mill KPW–25.